CROP WATER REQUIREMENT IN RELATION TO CLIMATE AND SOIL

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Abstract
The effect of variation in climate and soil on the production function of water for the yield of cotton, sorghum, and grapefruit was analyzed to determine the transferability of water requirement information, accumulated in Israel over the past 20 years on 20 field and orchard crops, to other regions of the world.A model giving relative yield (Y) as a linear function of relative evapotranspiration (Et/Eo) for all climatic regions together [Y = a + b(Et/Eo)], was compared with regional relationships of Y to net water application, (Di). Y is the ratio of a treatment yield to the maximum yield obtained in an experiment (y/ym); Et and Eo are the cumulative seasonal evapotranspiration, including a small drainage component, and pan evaporation, respectively. The same high correlation coefficient was found for both models, showing that about 90 percent of the variability in yield of field crops could be attributed to differences in potential evapotranspiration and in irrigation amounts. For grapefruit, the correlation coefficient was smaller.No effect was found of variations in soil on crop yield. This was due to the rather uniform water-storage capacity of soils of varying texture. Thus, for a wide range of soils, by taking into account variation in climate through the use of open water evaporation estimates (Class A pan), production functions obtained in Israel may be used in regions which similar climatic characteristics. The effect of variation in climate and soil on the production function of water for the yield of cotton, sorghum, and grapefruit was analyzed to determine the transferability of water requirement information, accumulated in Israel over the past 20 years on 20 field and orchard crops, to other regions of the world. A model giving relative yield (Y) as a linear function of relative evapotranspiration (Et/Eo) for all climatic regions together [Y = a + b(Et/Eo)], was compared with regional relationships of Y to net water application, (Di). Y is the ratio of a treatment yield to the maximum yield obtained in an experiment (y/ym); Et and Eo are the cumulative seasonal evapotranspiration, including a small drainage component, and pan evaporation, respectively. The same high correlation coefficient was found for both models, showing that about 90 percent of the variability in yield of field crops could be attributed to differences in potential evapotranspiration and in irrigation amounts. For grapefruit, the correlation coefficient was smaller. No effect was found of variations in soil on crop yield. This was due to the rather uniform water-storage capacity of soils of varying texture. Thus, for a wide range of soils, by taking into account variation in climate through the use of open water evaporation estimates (Class A pan), production functions obtained in Israel may be used in regions which similar climatic characteristics. © Williams & Wilkins 1978. All Rights Reserved.

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